Exactly Happens When You Start To Run
In the first few days and weeks of one’s running journey, the highly boasted of “runner’s high” may seem as elusive as Reputation, Taylor’s Version…
When is it coming?!
Does it even exist?!
How many more days, weeks, months do I have to wait?!
I want Rep. T.V and I want it NOW.
What most new runners do not fully appreciate (from both my own experience and the experience of those I’ve coached) is that the “runner’s high” is merely the tip of the iceberg in terms of all of the underlying changes that manifest in the first months of consistent run training. The practice of running is in fact, a whole-body transformation, right down to the cellular level. It is an activity that favours those who favour delayed gratification - those that persist through discomfort in the hope that one day things will be easier (just one of the many ways running is a lot like life, actually…)
It is easy to meet pain and suffering with frustration, particularly in this era of social media where the success, ease and achievements of those around us are so visible. HOWEVER… running is hard, regardless of when, where or how you start.
In the beginning, before the body has had time to adapt to the immense physical challenge of running, most runs feel uncomfortable. This is normal!
With an increased understanding of exactly what physiological, metabolic and emotional changes occur in the first six months of your running journey, you may develop an increased kindness towards yourself when that heart rate feels a lighter higher than what is comfortable, or those legs feel a little more tired than what you would expect.
The process of becoming a runner is hard! But you are strong, and you can do it!
The Cardiovascular System
The cardiovascular system (which includes both the heart and blood vessels that transport blood around the body) is one of the greatest beneficiaries of one’s running journey. It is the system that not only undergoes change most rapidly, but also leverages some of the greatest long-term benefits of physical activity.
Within minutes of starting to run, the sympathetic component of the nervous system, that is, the hormones that activate the “fight-or-flight” response (think of how you feel when you are scared, stressed or anxious…) causes the rate at which the heart pumps to increase. This increase in heart rate allows more blood to be delivered to organs that require a greater amount of oxygen whilst working hard - namely, the working muscles of the legs, the heart itself (yes, your heart actually is a muscle) and the brain. At the same time, blood is shunted away from organs that are less important in that specific moment, particularly the gut (hence the wide prevalence of nausea, vomiting, abdominal cramps, stitches and difficulty eating that many runners feel when they first start their journey).
Science Side
There is a concept in exercise physiology and medicine called cardiac output (CO). Cardiac output is essentially how much blood is being pumped around the body at any given time. There are two factors that contribute to cardiac output. These factors are:
Heart rate (HR) - the number of times a person’s heart beats per minute
Stroke volume (SV) - the volume (in millilitres) of blood that is ejected from the heart per pump
CO = HR x SV
Stroke volume is determined by many factors, which can be modulated over a period of weeks-to-months. Heart rate is much more variable, and can be changed on a second-to-minute basis. In somebody who is new to running, heart rate is the predominant variable that changes to increase overall cardiac output (which needs to increase during exercise to meet increased oxygen demands of working muscles). However, overtime, stroke volume - the volume of blood that is pumped out of the left ventricle of the heart per beat - increases. This is due to a combination of healthy growth of heart muscle (literally making it thicker and stronger), greater energy production within the muscle cells of the heart and greater volume of blood passing through the heart itself (due to overall increase in blood volume caused by exercise). Consequently, heart rate does not have to increase as much to maintain the same cardiac output. This is one of the reasons why some athletes have a resting heart rate as low as 30 to 40 beats per minute, and can keep their heart rate low-to-moderate whilst running at relatively high efforts.
As mentioned above, with ongoing exercise, adaptions occur within the muscles of both the heart and those required for running (e.g. quadriceps, hamstrings, calf muscles, hip flexors) that allow greater energy production. Energy is produced within a small part of the cell called the mitochondria.
More mitochondria = the ability to produce more energy = the ability to work harder, put out higher outputs, run for longer.
Key muscles also have more blood delivered to them by means of growth of new blood vessels. What starts as a “single highway” delivering oxygen via a gentle stream of blood, becomes a motorway with numerous side roads and feeding vessels, allowing blood to be delivered at higher volumes, more quickly. Both of these changes occur over a period of a few weeks, to one or two months, making running the same distance feel significantly easier over this period of time.
With consistent aerobic activity (that is, physical activity that uses oxygen to facilitate energy production - such as easy or steady running), various components of the heart undergo structural changes to facilitate higher cardiac output. This includes physiological hypertrophy of the left ventricle. Basically, the left ventricle (the main pumping component of the heart) undergoes healthy growth (as opposed to unhealthy growth, which can be considered a serious medical condition).
All in all, these changes to the cardiovascular system make running feel easier and less effortful in just a few short months.
The Musculoskeletal System
The musculoskeletal system (which includes the bony skeleton, muscles, tendons and ligaments) is perhaps the second greatest beneficiary of running. However, it is also one of the greatest barriers for people’s entry into running… how many times have you heard someone site sore knees or back pain as a reason for why they “can’t run?” The truth is - anyone who remains blessed with two feet can run - it is what humans were made to do! Mindset is what makes the difference.
Regardless, running is hard. Each time one of your legs hits the ground during a run, as much as eight times your body weight is transmitted through the knee joint!!
For someone who is completely new to this type of force, this is bound to cause some discomfort. However, there is no evidence to suggest that running directly causes degenerative conditions such as osteoarthritis. In fact, much the opposite is more likely to happen. Over a period of months, the tendons (which connect bone to bone) and ligaments (which connect muscle to bone) strengthen in response to the stress of running. In becoming strong, they become stiff, which helps to facilitate improved running form and biomechanics, again making running feel less tedious overall.
Other Systems
Despite the heart and skeletal muscles being centre stage of the post-running-transformation, the benefits of regular aerobic activity reach to almost every cell, tissue and organ within the body. Within a few weeks of running, the body shifts how it processes carbohydrates and fats to make fat more accessible as an energy source. The liver and skeletal muscles also hold on to stored glucose in the form of glycogen, creating a greater “back up” source of energy. This can be tapped into to facilitate longer, harder and more strenuous sessions. Other changes that occur over a longer period of time include:
Changes to the way the muscles and nerves communicate (this is called the neuromuscular junction) to allow for more efficient movements
Improved running form, as appropriate muscles grow and strengthen
More efficient use of oxygen for energy production (VO2 max) at higher efforts
Last, but not least, evidence within the last five years has found that the infamous runner’s high may more accurately be attributed to the release of hormones within the brain called endocannabinoids (as opposed to endorphins). Sharing a similar chemical structure to cannabis (yes..weed!!) these chemicals facilitate feelings of euphoria, less anxiety, reduced pain and increased stamina. Running has been noted to be the most effective physical activity for releasing endocannabinoids, followed by cycling, with only 20 minutes being a timeframe long enough to induce the aforementioned benefits.
TLDR
Running is a whole-body transformation, affecting numerous systems within the body.
Within a few minutes of running, heart rate increases to deliver more blood (which carries oxygen) to working muscles. Blood is shunted away from the gastrointestinal tract, causing nausea / vomiting, stitches and bowel problems.
Over a period of weeks to months, the heart adapts to pump more blood out with each beat. This is called stroke volume. A higher stroke volume is one of the cardinal changes secondary to aerobic exercise.
Eventually, the heart undergoes physiological hypertrophy. Essentially, the muscle thickens in response to ongoing physical activity, but not in a dangerous or pathological way.
Consistent running causes increased blood vessels to skeletal muscles, as well as the development of more mitochondria within cells. Mitochondria are little structures that are responsible for the production of energy.
Increased mitochondria = the ability to produce more energy - the ability to work hard, put out higher outputs and run for longer.
Over a period of months, tendons and ligaments thicken to absorb more force in response to the mechanical stress of running. In doing so, running form becomes more efficient.
The body also shifts its metabolism to be able to use free fatty acids as an energy source. Glycogen deposits within the liver and skeletal muscles become greater, allowing for a “back up” energy source during longer, harder efforts.
These metabolic, physiological and mechanical changes all occur over a period of weeks to months to make running more efficient and less effortful. Be patient with your body while it is changing so rapidly!